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Abstract: We have applied a method of reducing the number of iterations required to solve a system of linear equations in the discrete dipole approximation. This method obtains an initial guess of dipole polarization from those with similar particle characteristics (e.g., the size parameter and refractive index) calculated a priori. If the initial guess is closer to the solution, the number of iterations of the linear equation solution becomes smaller than that calculated with an arbitrary initial value. This method was applied to various particle orientations using spline interpolation of the initial guess of dipole polarization from orientations calculated a priori. We studied three types of particle model: an aggregate, a deformed sphere with moderate surface roughness, and a particle with a large number of edges. For the particle with a large number of edges, we propose a new model called the overlapping mixture of multiple tetrahedra (OMMT). The proposed method is most advantageous for particles with moderate surface roughness (e.g., a deformed sphere), for which the calculation time was reduced to 20–40% of the original calculation time. For OMMT and an aggregate, the computation time was reduced to 30–60% and 40–90%, respectively. The differences in the scattering coefficient, absorption coefficient, intensity and polarization introduced by our method were less than 0.008%, 0.03%, 0.1%, and 0.08%, respectively. If the light scattering properties vary slowly with the orientation variation, interpolation of the results is more efficient than the proposed method and produces only a small difference in the results. However, the interpolation of the results fails for particles such as BCCA64, for which our proposed method produces more accurate results. [Copyright &y& Elsevier]

Aerosol parameters are observed with a photopolarimeter (PSR-1000 device) and by SeaWiFS sensor during two research cruises conducted by R/V MIRAI in the equatorial Pacific regions. Observation of aerosol particles has shown the background characteristics of aerosol particles. The aerosol optical thickness calculated from PSR-1000 data coincide well with those from SeaWiFS data at 0.865 μm and shows difference at 0.443 μm. It is also shown that the data with low aerosol optical thickness has an ambiguity in the calculation of the Angstrom exponent for various sets of wavelengths. The refractive index of aerosol particles is retrieved by combining data from direct solar measurements and those from polarization measurements of scattered sun-light. [Copyright &y& Elsevier]

The review of optical instrumentation, forward modeling, and inverse problem solution for the polarimetric aerosol remote sensing from space is presented. The special emphasis is given to the description of current airborne and satellite imaging polarimeters and also to modern satellite aerosol retrieval algorithms based on the measurements of the Stokes vector of reflected solar light as detected on a satellite. Various underlying surface reflectance models are discussed and evaluated. [ABSTRACT FROM AUTHOR]

Abstract: We present a method to derive the light scattering properties of very porous fractal aggregates composed of a large number of monomers where the size parameter of monomer is larger than unity. Our new method is based on the grouping of the aggregate: The aggregate is divided into groups, where each group is located along a line of the incident light, and the scattering properties of the group are calculated taking into account multiple scattering with monomers located inside the group, as well as those in a buffer region around the group. The scattering and absorption efficiencies are obtained by adding the resultant scattering properties for all the groups. We have shown that the method effectively works when the monomer scatters the incident lights predominantly in the forward direction, which is the case if the monomer size is large compared to the wavelength of the incident light. The errors in resulting scattering and absorption efficiencies for porous aggregates are investigated for various refractive indices and sizes of monomers. We found that the errors are larger for low absorbing materials and they can be reduced by expanding the buffer region. In the case of the buffer region for each group consisting of 1/8 of the total number of monomers, the results show errors less than 15% and 10% for absorption and scattering, respectively. It is also shown that the errors have a small standard deviation (i.e., 2%) for different directions of the incident light. [Copyright &y& Elsevier]